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[2003:cb:c70e:5c00:522f:9bcd:24a0:cd70]) by smtp.gmail.com with ESMTPSA id n13sm4093040wrm.68.2022.01.28.00.10.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Jan 2022 00:10:21 -0800 (PST) Message-ID: Date: Fri, 28 Jan 2022 09:10:21 +0100 Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 To: Jonghyeon Kim Cc: dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20220126170002.19754-1-tome01@ajou.ac.kr> <5d02ea0e-aca6-a64b-23de-bc9307572d17@redhat.com> <20220127094142.GA31409@swarm08> <696b782f-0b50-9861-a34d-cf750d4244bd@redhat.com> <20220128041959.GA20345@swarm08> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 1/2] mm/memory_hotplug: Export shrink span functions for zone and node In-Reply-To: <20220128041959.GA20345@swarm08> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 28.01.22 05:19, Jonghyeon Kim wrote: > On Thu, Jan 27, 2022 at 10:54:23AM +0100, David Hildenbrand wrote: >> On 27.01.22 10:41, Jonghyeon Kim wrote: >>> On Wed, Jan 26, 2022 at 06:04:50PM +0100, David Hildenbrand wrote: >>>> On 26.01.22 18:00, Jonghyeon Kim wrote: >>>>> Export shrink_zone_span() and update_pgdat_span() functions to head >>>>> file. We need to update real number of spanned pages for NUMA nodes and >>>>> zones when we add memory device node such as device dax memory. >>>>> >>>> >>>> Can you elaborate a bit more what you intend to fix? >>>> >>>> Memory onlining/offlining is reponsible for updating the node/zone span, >>>> and that's triggered when the dax/kmem mamory gets onlined/offlined. >>>> >>> Sure, sorry for the lack of explanation of the intended fix. >>> >>> Before onlining nvdimm memory using dax(devdax or fsdax), these memory belong to >>> cpu NUMA nodes, which extends span pages of node/zone as a ZONE_DEVICE. So there >>> is no problem because node/zone contain these additional non-visible memory >>> devices to the system. >>> But, if we online dax-memory, zone[ZONE_DEVICE] of CPU NUMA node is hot-plugged >>> to new NUMA node(but CPU-less). I think there is no need to hold >>> zone[ZONE_DEVICE] pages on the original node. >>> >>> Additionally, spanned pages are also used to calculate the end pfn of a node. >>> Thus, it is needed to maintain accurate page stats for node/zone. >>> >>> My machine contains two CPU-socket consisting of DRAM and Intel DCPMM >>> (DC persistent memory modules) with App-Direct mode. >>> >>> Below are my test results. >>> >>> Before memory onlining: >>> >>> # ndctl create-namespace --mode=devdax >>> # ndctl create-namespace --mode=devdax >>> # cat /proc/zoneinfo | grep -E "Node|spanned" | paste - - >>> Node 0, zone DMA spanned 4095 >>> Node 0, zone DMA32 spanned 1044480 >>> Node 0, zone Normal spanned 7864320 >>> Node 0, zone Movable spanned 0 >>> Node 0, zone Device spanned 66060288 >>> Node 1, zone DMA spanned 0 >>> Node 1, zone DMA32 spanned 0 >>> Node 1, zone Normal spanned 8388608 >>> Node 1, zone Movable spanned 0 >>> Node 1, zone Device spanned 66060288 >>> >>> After memory onlining: >>> >>> # daxctl reconfigure-device --mode=system-ram --no-online dax0.0 >>> # daxctl reconfigure-device --mode=system-ram --no-online dax1.0 >>> >>> # cat /proc/zoneinfo | grep -E "Node|spanned" | paste - - >>> Node 0, zone DMA spanned 4095 >>> Node 0, zone DMA32 spanned 1044480 >>> Node 0, zone Normal spanned 7864320 >>> Node 0, zone Movable spanned 0 >>> Node 0, zone Device spanned 66060288 >>> Node 1, zone DMA spanned 0 >>> Node 1, zone DMA32 spanned 0 >>> Node 1, zone Normal spanned 8388608 >>> Node 1, zone Movable spanned 0 >>> Node 1, zone Device spanned 66060288 >>> Node 2, zone DMA spanned 0 >>> Node 2, zone DMA32 spanned 0 >>> Node 2, zone Normal spanned 65011712 >>> Node 2, zone Movable spanned 0 >>> Node 2, zone Device spanned 0 >>> Node 3, zone DMA spanned 0 >>> Node 3, zone DMA32 spanned 0 >>> Node 3, zone Normal spanned 65011712 >>> Node 3, zone Movable spanned 0 >>> Node 3, zone Device spanned 0 >>> >>> As we can see, Node 0 and 1 still have zone_device pages after memory onlining. >>> This causes problem that Node 0 and Node 2 have same end of pfn values, also >>> Node 1 and Node 3 have same problem. >> >> Thanks for the information, that makes it clearer. >> >> While this unfortunate, the node/zone span is something fairly >> unreliable/unusable for user space. Nodes and zones can overlap just easily. >> >> What counts are present/managed pages in the node/zone. >> >> So at least I don't count this as something that "needs fixing", >> it's more something that's nice to handle better if easily possible. >> >> See below. >> >>> >>>>> Signed-off-by: Jonghyeon Kim >>>>> --- >>>>> include/linux/memory_hotplug.h | 3 +++ >>>>> mm/memory_hotplug.c | 6 ++++-- >>>>> 2 files changed, 7 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h >>>>> index be48e003a518..25c7f60c317e 100644 >>>>> --- a/include/linux/memory_hotplug.h >>>>> +++ b/include/linux/memory_hotplug.h >>>>> @@ -337,6 +337,9 @@ extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, >>>>> extern void remove_pfn_range_from_zone(struct zone *zone, >>>>> unsigned long start_pfn, >>>>> unsigned long nr_pages); >>>>> +extern void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> + unsigned long end_pfn); >>>>> +extern void update_pgdat_span(struct pglist_data *pgdat); >>>>> extern bool is_memblock_offlined(struct memory_block *mem); >>>>> extern int sparse_add_section(int nid, unsigned long pfn, >>>>> unsigned long nr_pages, struct vmem_altmap *altmap); >>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>>>> index 2a9627dc784c..38f46a9ef853 100644 >>>>> --- a/mm/memory_hotplug.c >>>>> +++ b/mm/memory_hotplug.c >>>>> @@ -389,7 +389,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, >>>>> return 0; >>>>> } >>>>> >>>>> -static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> +void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> unsigned long end_pfn) >>>>> { >>>>> unsigned long pfn; >>>>> @@ -428,8 +428,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, >>>>> } >>>>> } >>>>> } >>>>> +EXPORT_SYMBOL_GPL(shrink_zone_span); >>>> >>>> Exporting both as symbols feels very wrong. This is memory >>>> onlining/offlining internal stuff. >>> >>> I agree with you that your comment. I will find another approach to avoid >>> directly using onlining/offlining internal stuff while updating node/zone span. >> >> IIRC, to handle what you intend to handle properly want to look into teaching >> remove_pfn_range_from_zone() to handle zone_is_zone_device(). >> >> There is a big fat comment: >> >> /* >> * Zone shrinking code cannot properly deal with ZONE_DEVICE. So >> * we will not try to shrink the zones - which is okay as >> * set_zone_contiguous() cannot deal with ZONE_DEVICE either way. >> */ >> if (zone_is_zone_device(zone)) >> return; >> >> >> Similarly, try_offline_node() spells this out: >> >> /* >> * If the node still spans pages (especially ZONE_DEVICE), don't >> * offline it. A node spans memory after move_pfn_range_to_zone(), >> * e.g., after the memory block was onlined. >> */ >> if (pgdat->node_spanned_pages) >> return; >> >> >> So once you handle remove_pfn_range_from_zone() cleanly, you'll cleanly handle >> try_offline_node() implicitly. >> >> Trying to update the node span manually without teaching node/zone shrinking code how to >> handle ZONE_DEVICE properly is just a hack that will only sometimes work. Especially, it >> won't work if the range of interest is still surrounded by other ranges. >> > > Thanks for your pointing out, I missed those comments. > I will keep trying to handle node/zone span updating process. The only safe thing right now for on ZONE_DEVICE in remove_pfn_range_from_zone() would be removing the given range from the start/end of the zone range, but we must not scan using the existing functions. As soon as we start actual *scanning* via find_smallest... find_biggest... in shrink_zone_span() we would mistakenly skip other ZONE_DEVICE ranges and mess up. Assume you would have a ZONE_DEVICE layout like [ DEV 0 | Hole | DEV 1 | Hole | DEV 2 ] What we actually want to do when removing * DEV 0 is scanning low->high until we find DEV 1 * DEV 1 is doing nothing, because we cannot shrink * DEV 2 is scanning high -> low until we find DEV 1 I assume we'd want to call in shrink_zone_span() two new functions for ZONE_DEVICE: find_smallest_zone_device_pfn find_biggest_zone_device_pfn Which would be able to do exactly that scanning, eventually, using get_dev_pagemap() or some similar source of information. -- Thanks, David / dhildenb